1. Technical Field
The present invention relates to an ink for forming a functional layer, an ink container, a discharging apparatus, a method for forming a functional layer, a method for manufacturing an organic electroluminescence (EL) element, a light emitting device, and an electronic apparatus.
2. Related Art
Recently, as a method for forming a colored layer (filter layer) of a color filter, a light emitting layer of an organic EL element, an electrode of a semiconductor such as an organic thin film transistor, or a functional layer such as a semiconductor layer, a method that uses a liquid phase process has been developed. In the liquid phase process, an ink jet method (also referred to as a droplet discharging method) has attracted attention, since the method is possible to apply accurately a predetermined amount of ink (solution) as a droplet at a desired position from a discharging head (ink jet head).
On the other hand, the ink (solution) which is used in the ink jet method causes to deposit solid contents on a nozzle of the discharging head due to drying and to clog the nozzle with solid contents, thus a discharging failure in which an impact position of the droplet varies and a discharged amount of the droplet discharged from the nozzle varies occurs. Therefore, the ink (solution) in which the discharging failure hardly occurs is required. Further, since a functional layer (functional film) is formed by applying and drying the ink (solution), it is required to evenly apply the ink on a desired area in an object to be applied such as a substrate.
For example, Japanese Patent No. 4616596 discloses that an ink composition for forming an amorphous film includes a first solvent of which a solubility of an organic material is more than or equal to 0.5 wt % and a second solvent that contains an alcohol compound of which a boiling point is higher than or equal to 120° C. in a solubility of less than or equal to 0.1 wt % of an organic material, in which the boiling point of the first solvent is higher than the boiling point of the second solvent. According to Japanese Patent No. 4616596, it is disclosed that the ink composition for forming an amorphous film is suitable for the ink jet method.
Furthermore, for example, in Japanese Patent No. 4707658, it is disclosed that an application liquid includes a mixed solvent and a functional material, in which the mixed solvent having two aromatic rings or more includes a first solvent that is formed by a compound having a symmetrical stricture and other solvent. If this application liquid is used, an occurrence of the nozzle clogging is difficult in the ink jet method, thus a stable discharge can be realized.
Moreover, for example, in Japanese Patent No. 5019454, it is disclosed that a solution of an organic semiconductor includes at least one kind of organic solvent A as a good solvent of the organic semiconductor and at least one kind of organic solvent B as a poor solvent of the organic semiconductor, in which a boiling point of the organic solvent A is higher than a boiling point of the organic solvent B. According to this solution, even film formation is possible since it is difficult to aggregate and deposit an organic semiconductor material during drying, thus an organic semiconductor having stable electrical properties can be formed.
However, in the ink composition of Japanese Patent No. 4616596, since the second solvent is the alcohol compound, there is a problem that the organic material is easily aggregated in a drying process of the applied ink composition. Furthermore, in Japanese Patent No. 4707658, since both of the first solvent and other solvent are aromatic compounds, there is a problem that a wetting spread is difficult and an uneven application easily occurs when the application liquid as a droplet is discharged on a conductive film such as a metal and a metal oxide. Moreover, in the solution of the organic semiconductor of Japanese Patent No. 5019454, since the boiling point of the organic solvent B is lower than the boiling point of the organic solvent A and a preferable ratio of the organic solvent B to the solution is less than or equal to 30 vol %, the organic solvent B evaporates earlier than the organic solvent A and an evaporating timing of the organic solvent B is relatively fast, in a drying process of the applied solution. Accordingly, there is a problem that wettability of the remaining organic solvent A as a good solvent is poor with respect to the object to be applied when the organic solvent A remains after evaporation of the organic solvent B and the uneven application easily occurs. In other words, in a solution configuration shown in Japanese Patent No. 4616596, Japanese Patent No. 4707658, and Japanese Patent No. 5019454, there is a problem that a functional layer (functional film) cannot be evenly formed.